It is known that certain metal complexes take up gases to form adducts from which those gases can be recovered. This is true of the cobalt(II) complex known as the Salen Chelate and related Fluomine chelate complexes; in addition, those complexes of the Vaska type, in which the metal is iridium, ruthenium, osmium, or rhodium, all take up oxygen reversibly. Under moderate conditions, the adducts do not release oxygen to regenerate the sorbent complexes sufficiently readily to enable oxygen to be produced or nitrogen to be purified on a commercial scale.
Complexes have now been found that take up gases to form adducts from which the gases can be readily recovered.